The proposed conference will be the third in a new series of Gordon Conferences on Three-dimensional Electron microscopy of Macromolecules. Electron microscopy has developed rapidly over the last few years as a tool for structure research at the molecular level. Important technical breakthroughs have been made which enable three-dimensional structure to be determined more accurately than before, and which open the way to a study of structure essentially under controlled physiological conditions. As a result, there are now exciting new opportunities for understanding biological mechanisms and principles of molecular design. The focus of this meeting will be on the novel electron microscopic methods being developed for preserving and imaging molecules in frozen solutions, for identifying specific sites on them by heavy atom labels, and for extracting near-atomic resolution three- dimensional information from images of molecules in isolation, in complex assemblies and in crystalline arrays. Important recent structural findings, relating especially to cell organelles, membrane and cytoskeletal proteins, will also be emphasized. This conference will help catalyze the further development of this field by bringing together many of the key investigators and allowing them to discuss their latest and perhaps even incomplete studies in a unique and informal setting. Speakers are being chosen on the basis of the importance of their recent research contributions and the potential of their particular approach in future structure research. Topics to be covered include: cryoelectron microscopy, new methods in averaging, three-dimensional reconstruction, use of site-specific labels, image correlation and classification (sorting), and recent structural results obtained for membranes, filaments, organelles, and viruses.